1. Field of the Invention
The present invention relates to a laser radar system for irradiating laser light to detect a state of a target area, a beam irradiation device suitably used in the laser radar system, and a detecting device for detecting a position of a movable object.
2. Description of the Related Art
In recent years, a laser radar system has been loaded in a family automobile or a like vehicle to enhance security in driving. Generally, the laser radar system is configured in such a manner that a target area is scanned with laser light to detect whether there is an obstacle at each of scanning positions, based on presence or absence of reflection light at each of the scanning positions; and that a distance to the obstacle at the scanning position is measured based on a time period from the point of time when the laser light is irradiated to each of the scanning positions to the point of time when the reflection light at the scanning position is received.
It is necessary to properly scan a target area with laser light to increase detection precision of a laser radar system. It is also necessary to properly detect each of scanning positions by laser light.
A scanning position can be detected by e.g. separating a part of laser light to be irradiated onto a target area by a beam splitter or a like device, and receiving the separated light (servo light) by a photodetector (a light receiving position detecting device) such as a PSD (Position Sensitive Detector)for use in position detection.
In the above arrangement, the laser radar system has a lens actuator for moving a scanning lens for receiving laser light in a direction orthogonal to an optical axis of laser light. Driving the lens actuator allows for scanning a target area with laser light.
With use of the lens actuator, the scanning position can also be detected by directly detecting a moved position of the scanning lens. In order to perform the above operation, for instance, there is proposed an arrangement, wherein a laser light source for emitting servo light is mounted on a lens holder for supporting a scanning lens to receive servo light from the laser light source by a light receiving position detecting device (PSD).
In the above arrangement, increasing the moving amount of the scanning lens to increase the amplitude of laser light in a target area may increase the amplitude of servo light. This may require a light receiving position detecting device having a relatively large light receiving surface, and increase the cost of the laser radar system. Also, in the case where servo light is condensed on the light receiving position detecting device, a large-sized condenser lens is necessary to condense servo light having a certain magnitude of amplitude on the light receiving position detecting device. This may increase the cost of a laser radar system and the size of an optical system.